(1) Field of the Invention
The present invention relates to a connecting rod bearing (i.e. a slide bearing) for internal combustion engines, which rotatably supports a crankpin connecting a connecting rod and a crankshaft, wherein lubricant oil is supplied to an inner surface of a main bearing, which supports the crankshaft, and further to an inner surface of the connecting rod bearing through an internal lubricant-oil passage formed in the crankshaft.
(2) Related Art
A crankshaft of an internal combustion engine is supported in a lower section of a cylinder block of the internal combustion engine at a journal section thereof through a main bearing consisting of a pair of semi-cylindrical bearings. In the main bearing, lubricant oil discharged from an oil pump is fed into an oil groove, being formed on the inner surface of the main bearing, through an oil gallery formed in the cylinder block wall and a through hole formed in the main bearing wall. A first lubricant-oil passage is diametrically formed through the journal section, and openings at the both ends of the first lubricant-oil passage are in fluid communication with the oil groove. Further, a second lubricant-oil passage is formed in the crankshaft so as to branch off from the diametrical first lubricant-oil passage in the journal section to go through a crank arm, which second lubricant-oil passage is in fluid communication with a third lubricant-oil passage diametrically formed through a crankpin. Thus, the lubricant oil fed from the oil gallery in the cylinder block wall via the through hole formed in the main bearing wall into the oil groove formed on the inner surface of the main bearing flows through the first, second and third lubricant-oil passages, and be supplied between sliding surfaces of the crankpin and a connecting rod bearing from outlet ports at both ends of the third lubricant-oil passage (which is a lubricant-oil outlet port existing on the surface of the crankpin).
The lubricant oil fed from the cylinder block of the internal combustion engine through the journal section of the crankshaft to the connecting rod bearing might carry foreign substances remaining in the respective lubricant-oil passages. If such foreign substances entrained by the lubricant oil are fed between the crankpin and the connecting rod bearing, there is a risk that the foreign substances damage the sliding surface of the connecting rod bearing. Thus, it is needed to quickly discharge the foreign substances from the sliding surface of the crankpin and the connecting rod bearing to outside.
As a countermeasure against the foreign substances accompanied with the lubricant oil, there has been a proposal to discharge the foreign substances by providing a circumferential oil groove throughout the entire circumferential length of the inner surface of one of the semi-cylindrical bearings of the main bearing which consists of a pair of the semi-cylindrical bearings and which supports the journal section of the crankshaft, the one of the semi-cylindrical bearings having a through hole which directly receives the lubricant oil supplied from the oil gallery in the cylinder block wall. When the above idea is applied to the connecting rod bearing, however, it was confirmed by an experiment that not only the foreign substance discharge effect is obtainable but also the proposed way is counterproductive since the foreign substances remain in the circumferential oil groove formed throughout the entire circumferential length of the inner surface of the semi-cylindrical bearing of the connecting rod bearing, and are dispersed throughout the sliding surface of the bearing thereby becoming liable to damage the bearing.
This is because in general a housing, which holds the connecting rod bearing, is considerably deformed during engine operation, so that a clearance between the crankpin and the connecting rod bearing during the engine operation is larger than a clearance between the journal section of the crankshaft and the main bearing, so that the foreign substances remaining in the oil groove are liable to be dispersed throughout the sliding surface of the bearing including “a circumferential center section of the semi-cylindrical bearing” as a primary load receiving section. Such a connecting rod bearing suffers increased damages as compared with a conventional connecting rod bearing without such a circumferential oil groove. This was confirmed by an experiment.
Therefore, in order to discharge foreign substances flowing onto the sliding surface of the connecting rod bearing together with the lubricant oil from the lubricant-oil outlet port on the crankpin surface, the present inventor has proposed the connecting rod bearing in which at least in one of a pair of semi-cylindrical bearings constituting the connecting rod bearing, a front side circumferential groove is formed along the bearing inner circumferential surface from the front side circumferential end surface which is positioned at a front side with respect to the rotational direction of the crankpin, and the axial groove which communicates with the front side circumferential groove is formed throughout the entire length of the width in the axial direction along the bearing inner circumferential surface (JP-A-2009-174697). According to the configuration, the foreign substances accompanying the lubricant oil supplied from the lubricant-oil outlet port located on the outer surface of the crankpin are caught by the front side circumferential groove, and are fed to the vicinity of the circumferential end surface together with the lubricant oil along the front side circumferential groove. Subsequently, the foreign substances are blocked by the circumferential end surface of the opposed semi-cylindrical bearing, and the foreign substances are prevented from flowing onto the sliding surface of the opposed semi-cylindrical bearing. The foreign substances blocked by the circumferential end surface of the opposed semi-cylindrical bearing flow into the axial groove and are discharged to the outside of the bearing.
In the internal combustion engines of recent years, oil pumps have been miniaturized in order to reduce fuel consumption, the amounts of the lubricant oils supplied to the bearing sliding surfaces have been reduced as compared with the conventional internal combustion engines, and shortage of supply of the lubricant oil to the bearing sliding surface have occurred.
Excellence in foreign substance discharging property and excellence in suppliability of the lubricant oil onto the bearing sliding surface are required for the connecting rod bearings of internal combustion engines.
Here we would raise the following patent publications of the related art:    1. JP-A-8-277831    2. JP-A-2005-69283    3. JP-A-2009-174697